After having done all I know to do in converting my 406 automatic to manual it won't start. I am lost as to what to do with the automatic gearbox electrical loom hanging loose. How do I go about it for I am not an electrical expert? Any sensors which have to be disconnected for my car to start? Before the conversion there was no problem with starting the engine.

  • Welcome to Motor Vehicle Maintenance & Repair! Does it do anything when you turn the key? Does the engine turn over, but not start, or does it not turn over at all? Does the fuel pump kick on when you first turn the key? You have power to accessories? Mar 18, 2018 at 1:51
  • If you left the autobox loom hanging loose, did you bypass / correct / disable the safety circuit where autoboxes will only start in park / neutral?
    – Solar Mike
    Mar 18, 2018 at 6:03

1 Answer 1


The Peugeot 406 uses a Transmission control module, did you disconnect this or did you leave it in place? It is located next to the Engine ECU.

Firstly you need to find the Transmission Park Interlock relay, then connect wires D01A & D01B (pins 3B&5B) together, you can't rely on Peugeot wire colours you must read the numbers on the wires. Or just connect wire up a standard relay between the starter motor solenoid and the ignition switch.

Wires 6745 & CM04K (pins 3A & 5A) and the other wires connected to the relay can be removed or left as is.

Pin A1&2 (wires CM04G & 220) from the Transmission Control module are for the reverse light switch.

That should be all that is required to make it start and, it would be a nice job to remove every other wire that is no longer required to avoid short circuits, it also just makes it easier for future wiring and electrical jobs.

You may however get the check engine light due to it not being able to 'talk to' the TCM, you can either put up with this or get the ECU reprogrammed by a good auto-electrician or tuner, the dealer won't be able to do this.

  • If all else is equal between auto/manual models, would the OP also be able to drop in a manual 406 ECU? Or would that be more work than just tricking the current ECU? Mar 18, 2018 at 22:02
  • It would be the same if not more work, as the immobiliser and VIN number are coded to the engine ECU so you would need to do the same programming to the auto ECU as you would to the original. Mar 19, 2018 at 19:29
  • That’s kind of what I figured would be the case. Mar 19, 2018 at 19:46

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